1. Technical Field
The present invention relates in general to an improved means of processing sliders for hard disk drive read/write heads, and in particular to an improved means of reducing damage to and contamination of hard disk drives, especially during load/unload operations of the sliders on the disks, but also potentially during any other conditions that may cause slider-disk contact.
2. Description of the Prior Art
In hard disk drives, the use of load/unload (L/UL) designs has become increasingly popular. In L/UL designs, the slider is “loaded” down a ramp onto the spinning disk prior to any data reading and writing operations, and “unloaded” off of the disk back onto the ramp when the reading and writing operations are complete. This approach reduces the problems of head-disk stiction and media damage from shock as the fly height (e.g., the height at which a slider flies above the surface of a spinning disk) continues to decrease. These designs also have the advantage of reducing power consumption.
However, due to high disk and load/unload speeds, L/UL schemes potentially risk media damage from slider-disk contact during loading and/or unloading. Research has shown that this damage is specifically associated with the sharp corners and/or edges of the block-like sliders digging into the disk surface upon impact. The resulting damage in the L/UL zone of the disk makes this region unsuitable for data storage, thereby reducing the overall storage capacity of the drive by 5 to 15%. In addition, the particles or debris that are created during the slider-disk impacts may decrease the overall reliability of the drive.
The problem of disk damage during L/UL can be reduced by designing the air bearing, suspension, ramp, and disk drive parameters (e.g., disk and L/UL speeds) such that head-disk contact is eliminated or reduced. Alternatively, the slider itself can be processed in such a way that any contact that does occur causes no damage or an acceptably small amount of damage to the disk. Rounding (which also is referred to as “blending”) slider corners and/or edges so that no sharp points (regions of high stress concentration) are presented to the disk surface during contact, is a demonstrated way to reduce disk damage from L/UL. Slider corner and/or edge rounding may have the added benefit of reducing disk damage associated with mechanisms other than L/UL, such as reading or writing in the presence of operational shock, disk defects, or particles. By reducing the severity of slider-disk impacts, corner and edge rounding can additionally reduce particle generation in the drive, and thereby improve drive reliability. Yet another benefit might result from rounding, smoothing, or chamfering the rough, saw-cut edge of the slider and removing any poorly-attached particles that would otherwise be released into the drive upon contact.
In the prior art, a number of mechanical techniques have been used to produce rounded corners and edges on sliders. For example, the exposed corners and/or edges of a slider have been burnished, one at a time, with abrasive plates or abrasive tape that has been stretched over the slider. Methods which are directed to processing individual ones of the sliders were popular when slider form factors were larger and throughput constraints were not as rigorous.
Another prior art method attempted bulk rounding of single flat rows of sliders that were parted or semi-parted. The abrasive tape is presented at an angle to the single row of sliders or, equivalently, the slider or row is presented at an angle to the tape. If ample clearance is provided between the rows of sliders, this technique allows the tape to comply around the slider corners and edges. Rubbing or vibratory motion of the abrasive tape relative to the slider or row burnishes the corners and edges. Japanese Publication Nos. JP2000094292-A and JP2000094294-A, are directed to methods of this type. In these approaches, a row of sliders that is placed in a rigid holder (probably the transfer tool on which the sliders were parted) is pushed by a load addition unit onto a rubber-backed abrasive sheet at an angle. Wires extending between the sliders push and deform the abrasive sheet into the clearances between the completely flat array of sliders to enable beveling of the slider edges.
Each of these prior art methods of burnishing slider corners and edges have significant disadvantages. The single slider methods are too slow to allow cost-effective bulk manufacturing. The cost and throughput considerations generally mandate placing sliders as close together as possible on a row. With such limited clearances, it is very difficult to burnish between the rows of sliders on a rigid fixture, even if the wires of the two Japanese publications are used to push the abrasive sheet into these spaces. Bulk rounding on a rigid fixture is inflexible. Depending on the particular row or slider configuration, sensitive structures may be damaged by the mechanical action of the abrasive due to their unavoidable proximity to such structures. Implementation of bulk rounding on a rigid fixture is complex and expensive, and is only cost-effective for a particular manufacturing process (e.g., one in which rows are parted into sliders with relatively large clearances on a rigid transfer tool). Moreover, these methods have no ability to adjust individual slider orientations to provide flexible rounding geometries, and they only work with sufficiently large slider kerf.
Still other prior art, alternative methods that have been used for slider corner/edge rounding have included crowning sliders with elevated rim caps (see International Publication No. WO200043992-A1), laser melting or ablation, and rounding using mechanical or chemical etching. The latter method is proposed in Japanese Patent No. JP11219574-A, wherein a thin film magnetic head slider structure has a small curved surface formed on a flotation surface of the slider by ion milling or dry etching.
Unfortunately, each of these approaches also has significant problems. Methods that utilize lasers are generally hampered by the creation of melted and re-solidified material around the melted or ablated area. This “slag” material can often protrude significantly above the rest of the surface, making the resulting sliders unusable given the extremely small slider-disk separations in a disk drive. In addition, it is very difficult to control the rounding produced by laser melting or ablation to the tolerances required. The shapes produced by etching processes are also difficult to accurately control. In addition, both laser and etching processes most easily produce tapered corners or edges rather than the more rounded profiles that are most effective at reducing disk damage. The depths that are readily achievable with some etching processes are limited by constraints of sample heating, depending on the tool and part configurations. Finally, etching processes are not as effective as mechanical burnishing processes in reducing roughness in the rounded regions of sliders. Thus, a mechanical burnishing apparatus and method that can more easily produce slider corner/edge profiles that are smoother, more controllable, and rounded than laser or etching approaches would be highly desirable.